Field of the Invention
This invention pertains generally to treating infections caused by gram-negative bacteria. More specifically, the invention described herein pertains to treating gram-negative infections by inhibiting activity of UDP-3-O—(R-3-hydroxydecanoyl)-N-acetylglucosamine deacetylase (LpxC). The present invention provides small molecule inhibitors of LpxC, pharmaceutical formulations containing such inhibitors, methods of treating patients with such pharmaceutical formulations, and methods of preparing such pharmaceutical formulations and inhibitors. The inhibitors can be used to treat gram-negative infections of patients alone and in combination with other antibacterials.
Description of the Related Art
Over the past several decades, the frequency of antimicrobial resistance and its association with serious infectious diseases have increased at alarming rates. The increasing prevalence of resistance among nosocomial pathogens is particularly disconcerting. Of the over 2 million nosocomial infections occurring each year in the United States, 50 to 60% are caused by antimicrobial-resistant strains of bacteria. This high rate of resistance increases the morbidity, mortality, and costs associated with nosocomial infections. In the United States, nosocomial infections are thought to contribute to or cause more than 77,000 deaths per year and cost approximately $5 to $10 billion annually. Among gram-positive organisms, the most important resistant pathogens are methicillin-(oxacillin-)resistant Staphylococcus aureus, β-lactam-resistant and multidrug-resistant pneumococci, and vancomycin-resistant enterococci. Important causes of gram-negative resistance include extended-spectrum β-lactamases (ESBLs) in Klebsiella pneumoniae, Escherichia coli, and Proteus mirabilis, high-level third-generation cephalosporin (Amp C) β-lactamase resistance among Enterobacter species and Citrobacter freundii, and multidrug-resistance genes observed in Pseudomonas aeruginosa, Acinetobacter, and Stenotrophomonas maltophilia (see Jones, R. N., “Resistance patterns among nosocomial pathogens: Trends over the past few years” Chest., 2001, 119 (Supp 2), 397S-404S).
The problem of antibacterial resistance is compounded by the existence of bacterial strains resistant to multiple antibacterials. For example, Pseudomonas aeruginosa isolates resistant to fluoroquinolones are virtually all resistant to additional antibacterials (see Sahm, D. F. et al., “Evaluation of current activities of fluoroquinolones against gram-negative bacilli using centralized in vitro testing and electronic surveillance” Antimicrobial Agents and Chemotherapy, 2001, 45, 267-274).
Thus there is a need for new antibacterials, particularly antibacterials with novel mechanisms of action. Most of the antibacterial discovery effort in the pharmaceutical industry is aimed at development of drugs effective against gram-positive bacteria. However, there is also a need for new gram-negative antibacterials. Gram-negative bacteria are in general more resistant to a large number of antibacterials and chemotherapeutic agents than are gram-positive bacteria. A survey of recently reported antibacterials of natural origin showed that over 90% lacked activity against Escherichia coli, although they were active against gram-positive bacteria. The outer membrane of gram-negative bacteria contributes to this intrinsic resistance by acting as an efficient permeability barrier, because the narrow porin channels limit the penetration of hydrophilic solutes and the low fluidity of the lipopolysaccharide leaflet slows down the inward diffusion of lipophilic solutes. A second mechanism also contributes to the intrinsic resistance of gram-negative bacteria. Recent studies showed that multiple drug efflux pumps, sometimes with unusually broad specificity, act as this second factor to create the general intrinsic resistance of gram-negative bacteria. When their expression levels are elevated as a consequence of physiological regulation or genetic alteration, they can frequently produce impressive levels of resistance to a wide variety of antimicrobial agents (see Nikaido H., “Antibacterial resistance caused by gram-negative multidrug efflux pumps” Clinical Infectious Diseases, 1998, 27 (Supp 1), S32-41).
Historically, most development of antimicrobial agents has been relatively empirical. Active compounds have generally been found via screening soil, sewage, water, and other natural substances to detect antimicrobial-producing organisms, or by screening various chemical compounds. Once a leading candidate has been found and its chemical structure determined, a series of analogs is made to identify an optimal compound for further clinical development. A more rational approach involves the defining of new targets, such as genes or enzymatic functions, responsible for a crucial cellular essential activity. Once this has been done, inhibitors or blockers of the function or gene product can be developed.
In order to identify potential targets for novel gram-negative antibacterial agents, studies aimed at identifying all essential and important genes in Pseudomonas aeruginosa have been performed. Among the essential genes identified was LpxC, that encodes the enzyme uridyldiphospho-3-O—(R-hydroxydecanoyl)-N-acetylglucosamine deacetylase (LpxC). This enzyme is the first committed step in the synthesis of lipid A, the lipid moiety of lipopolysaccharide, that is an essential component of all gram-negative bacteria. It therefore is an attractive target for novel antibacterials. In order to be useful as antibacterial agents, LpxC inhibitors would not only have to inhibit the enzymatic activity of LpxC from a variety of bacteria, but would have to defeat the intrinsic resistance mechanisms of gram-negative bacteria, as described above (i.e., they would have to penetrate the outer membrane and be relatively unsusceptible to multidrug efflux pumps).
To date, researchers have identified a few compounds with antibacterial activity that target lipid A biosynthesis. For example, International PCT Publication No. WO 97/42179 to Patchett et al. discloses compounds of the formula:
The compounds possess activity against certain gram-negative organisms, for example Escherichia coli, but are not active against other medically important gram-negative bacteria, for example Pseudomonas aeruginosa. Subsequent studies have found that the primary reason for their inactivity against particular, medically important gram-negative bacteria is their poor ability to inhibit P. aeruginosa LpxC; efflux by the major multidrug efflux pump or inability to penetrate the outer membrane were not the critical factors.
Jackman et al. (J. Biol. Chem., 2000, 275(15), 11002-11009) discuss the mechanism of lipid A biosynthesis in the context of gram-negative bacteria and disclose a new class of hydroxamate-containing inhibitors of LpxC. Wyckoff et al. (Trends in Microbiology, 1998, 6(4), 154-159) discuss the role of LpxC in lipid A biosynthesis and its role in regulation and disclose a few oxazoline hydroxamic acids that inhibit bacterial growth. However, Wyckoff et al. also discuss the shortcomings of the available deacetylase inhibitors as bactericidal agents against Pseudomonas and note that more work is needed to be done in the area.
U.S. Patent Application Publication No. 2001/0053555 (published Dec. 20, 2001, corresponding to International PCT Publication No. WO 98/18754 published May 7, 1998) discloses a combinatorial library of hydroxylamine, hydroxamic acid, hydroxyurea and hydroxylsulfonamide compounds purported to be potentially useful as inhibitors of metalloproteases, and U.S. Pat. No. 6,281,245 claims a method of inhibiting a deformylase enzyme by administering one of the hydroxylamine compounds from the combinatorial library disclosed in U.S. Patent Application Publication No. 2001/0053555. Related to the foregoing patent publications is International PCT Publication No. WO 99/57097 (published Nov. 11, 1999) that discloses a method of solid phase synthesis of the hydroxyl amine library of compounds.
International PCT Publication No. WO 00/61134 to British Biotech Pharmaceuticals Limited (published Oct. 19, 2000) discloses compounds of the formula:
The compounds are useful as antimicrobial agents and are believed to have bactericidal activity due, at least in part, to intracellular inhibition of bacterial polypeptide deformylase.
In earlier International PCT Publication No. WO 99/39704 to British Biotech Pharmaceuticals Limited (published Aug. 12, 1999), compounds of the following formula were disclosed:
The compounds are useful as antimicrobial agents useful against gram-negative and gram positive bacteria.
De Novo Pharmaceuticals LTD disclosed in International PCT Publication No. WO 02/50081 (published Jun. 27, 2002), certain antibacterial and antiprotozoal agents having the formulae shown below:
The patent publication discusses that the antibacterial activity is due, at least in part, to intracellular inhibition of bacterial polypeptide deformylase.
More recently, certain compounds having activity against gram-negative bacterial infections were disclosed in U.S. Patent Application Publication No. 2004/0229955 (published Nov. 18, 2004).
Although there have been advances in the field, there remains a need for LpxC inhibitors that have activity as bactericidal agents against gram-negative bacteria. It is, accordingly, an object of this invention to provide compounds and combinations of such compounds for use in the preparation of antibacterials and other pharmaceuticals capable of inhibiting gram-negative bacterial infections.